I realize people have already answered - and they are absolutely right - but I heard about something else you might find interesting. It's a small selection of information a tagahanga collected prior to the sequel's release:
link I'm afraid I don't know how accurate this is because I didn't see the original article, and it sounds like the magazine got certain bits of information very wrong anyway! But it seems like Kovu's character was originally going to be Scar's son. At some point the writers must have realized, "wait, she can't marry her dad's cousin!" and changed this (along with other details of the storyline). Though like I said, considering they wrote that Simba and Scar were brothers, I don't know how trustworthy the rest of the artikulo is. Thought you might find it interesting though!
